Method for the production of an automotive exhaust gas catalyst

ABSTRACT

A method for preparing a catalyst suitable for use in a catalytic system for oxidation of air pollutants in automotive exhaust gases, such method comprising, in combination, the steps of mixing and kneading a nickel source and a chromium source, and, as a binder, a member selected from the group consisting of an alumina sol and a soluble aluminum hydroxide, and, as a carrier, activated alumina, molding the resulting mixture with a catalyst molder into a desired shape, drying the formed material, impregnating the dried formed material with a solution of a palladium salt, drying the thus impregnated formed material, and thereafter calcining same.

it ttes ichihara et al.

aet 1 [4 1 Jan. 22, 1974 4] METHOD FOR THE PRODUCTION OF AN AUTOMOTIVEEXHAUST GAS CATALYST [73] Assignee: Nippon Sholtubai Kogyo Co., Ltd.,

Higashi-ku, Osaka, Japan [22] Filed: Nov. 16, 1971 21 Appl. No.: 199,378

[52] US. Cl. 252/465, 252/466 B, 453/213 [51] Int. Cl Btllj 11/06, BOlj11/12 [58] Field of Search 252/465, 466 B; 423/213 [56] References CitedUNITED STATES PATENTS 3,133,029 5/1964 Hoekstra 425/213 X 3,493,3252/1970 Roth 252/465 X 3,397,154 8/1968 Talsma 252/465 X 3,437,426 4/1969Quesada 252/466 B 9/1969 Briggs et al. 252/465 X Primary Examiner-DanielE. Wyman Assistant Examiner-W. J. Shine Attorney, Agent, or FirmLeonardW. Sherman et al.

[5 7] ABSTRACT A method for preparing a catalyst suitable for use in acatalytic system for oxidation of air pollutants in automotive exhaustgases, such method comprising, in combination, the steps of mixing andkneading a nickel source and a chromium source, and, as a binder, amember selected from the group consisting of an alumina sol and asoluble aluminum hydroxide,

and, as a carrier, activated alumina, molding the resulting mixture witha catalyst molder into a desired shape, drying the formed material,impregnating the dried formed material with a solution of a palladiumsalt, drying the thus impregnated formed material, and thereaftercalcining same.

26 Claims, No Drawings METHOD FOR THE PRODUCTION OF AN AUTOMOTIVEEXHAUST GAS CATALYST This invention relates to a method of producing anickel oxide-chromium oxide-palladium oxide-alumina catalyst for use inclarifying the exhaust gases of internal combustion engines by the useof which catalyst the complete oxidation of the fuel mixture iseffected. More specifically, the invention relates to a method ofproducing the foregoing catalyst, which when used for the treatment ofthe exhaust gases containing carbon monoxide (CO) or residualhydrocarbons (HC) resulting from the incomplete combustion of the fuelin the engine completely oxidizes these components to harmless carbondioxide and water to thus effect the clarification of the exhaust gases.

The recent rapid increase in the number of automobiles on the road hasgiven rise to a serious environmental pollution problem. This problem ofair pollution is especially serious in the urban areas, and an immediatesolution to the problem is desired. It is well known that a majorportion of the organic pollutants in air originates from the unburned orpartially burned automotive exhaust gases. It is also well known that itis a very difficult to eliminate these organic substances physically.

Thus, various methods of eliminating these organic substances are beinginvestigated, one of which is the method of completely oxidizing the COand HC by means of a catalyst; i.e., a method of oxidizing the CO and HCto harmless carbon dioxide and water by passing the exhaust gasesthrough a catalyst layer. However, in order that this oxidizing catalystcan fully demonstrate its performance on being fitted to an internalcombustion engine, it is required to further satisfy the followingconditions from the standpoint of its practical use.

1. It must possess activity at low temperatures as well as resistance toheat.

2. it must be able to maintain its catalytic activity notwithstandingfluctuations in the rate of flow of the gas, the gas composition and theexhaust temperature.

3. It must function though the contact time is short, since there is thelimitation as to space in view of the fact that the catalytic mufflermust be mounted in a confined space below the floor of the automotivebody.

4. Its resistance to attrition must be great, since it is to be mountedto the automotive chassis which is constantly subjected to vibrations.

5. It must possess resistance to such materials as carbon and the mistof lubricating oil, since contact occurs with these substances.

6. It must possess adequate life so as to be able to endure for aprolonged period of operation of the automobile.

The rate of flow of the exhaust gas of an engine, the compositions ofthe gas and the exhaust temperature fluctuate broadly. For instance, inthe case of the rate of the flow of the exhaust gas, the differencebetween the minimum and maximum rates fluctuates up to several tens oftimes depending upon the operating condi tions of the engine, andsimilarly the exhaust temperature also fluctuates from room temperatureto a maximum of close to l,000C. Further, since a temperature rise dueto the endothermic reaction inside the catalyst is added, of theforegoing conditions the resistance to heat and activity at lowtemperatures are of special importance.

The object of the present invention is therefore to provide an exhaustcatalyst which can meet the forego ing conditions. 1

Research was conducted concerning various catalysts while givingconsideration to the conditions indicated hereinabove, with theconsequence that it was found that a catalyst obtained by molding acatalyst substance consisting of nickel oxide, chromium oxide andpalladium oxide in a specified ratio and as a carrier finely dividedactivated alumina, along with an alumina type binder excelled inoxidizing activity as well as durability, and therefore the inventionwas perfected.

Thus, in accordance with the present invention a method for preparing acatalyst suitable for use in a catalytic system for the oxidation of airpollutants in automotive exhaust gases is provided, such methodcomprising mixing and kneading a nickel source and a chromium source inwhich the atomic ratio of nickel to chromium is 1:1 l2 and the amountsthereof are such that the total amount of nickel oxide and chromiumoxide contained in the catalyst to be finally obtained is 5 30 and, as abinder, either alumina sol or a soluble aluminum hydroxide in an amount,based on the weight of the catalyst to be finally obtained, of 2 20calculated as alumina and, as a carrier, an activated alumina whoseparticle size distribution is in the range of 2 300 microns and averageparticle diameter is not greater than 110 microns, molding the resultingmixture into a desired shape with a catalyst molder, drying theformedmaterial at a temperature not exceeding 150C, followed bycalcining it at a temperature not exceeding 800C., or omission of thisstep, then impregnating the formed material with a palladium saltsolution in an amount, based on the weight of the catalyst to be finallyobtained, of 0.01 0.l calculated as palladium, and thereafter drying theimpregnated material at a temperature not exceeding l50C. followed bycalcining same at a temperature not exceeding 800C. for 3 15 hours.

The activated aluminas used in the present invention are convertedaluminas which have not yet reached the alpha-alumina stage and arethose obtained by calcining aluminum hydroxide. They usually have asurface area exceeding square meters per gram. Of these, preferred fromthe standpoint of heat resistant stability, activity and tackinessduring the molding of the catalyst are the pseudogamma, eta and chitypes of-alumina. On the other hand, with respect to particle size, fromthe standpoint of catalytic activity and moldability those preferablyused are those whose particle size distribution falls within the rangeof 2 300 microns and whose average particle diameter is not greater thanmicrons, and preferably not greater than 50 microns.

As convenient sources of nickel, mention can be made of the acetate,bromide, chloride, nitrate, oxalate, forrnate, carbonate, hydroxide,oxide, etc., of nickel. Since a nickel source not possessing solubilitymust be used as a slurry, those which are preferred are of finelydivided form, e.g., those of particle diameter not greater than 110microns.

As a convenient source of chromium, included are ammonium chromate,chromic acid, ammonium dichromate, and the nitrate, acetate, chloride,carbonate,

hydroxide, oxide, etc., of chromium. Since a chromium source notpossessing solubility must be used in a slurry state, best results arehad by using this also in a finely divided state of not greater than 1microns as in the case with the nickel source.

The use of palladium even in a small amount of 0.01 0.1 based on thecatalyst to be finely obtained, imparts good activity in this invention.Especially in the case where the palladium has been dispersed on onlythe catalyst surface, good activity is demonstrated even though theamount is exceedingly small. Convenient palladium sources are the saltssuch as bromide, chloride and nitrate of palladium.

On the other hand, either an alumina sol or a soluble aluminum hydroxideis necessary as a binder for molding the catalyst into a molded producthaving great strength. As the alumina sol, conveniently useable are thecommerically available acetic acid, formic acid and hydrochloric acidacidified aluminas. As the colloidal aluminum hydroxide, which is knownas a soluble aluminum hydroxide sol, conveniently useable is thealuminum hydroxide having a fibrous boehmite structure which dispersescolloidally when introduced into a liquid, e.g., such as Baymal, aproduct of Du Pont Company.

In the preparation of the invention catalyst, the use of siliceoussubstances must be avoided, since they impair the activity, andespecially the low temperature activity, of the catalyst. Again, the useas the starting material of substances which contain as impurities thealkali metals such as sodium, potassium, etc., and alkaline earth metalssuch as calcium, etc., must be avoided in preparing the inventioncatalyst. The reason is because difficulty is experienced in removingthese metals even though washing and filtration operations arerepeatedly carried out and, in addition, the catalysts which contain thesalts of these metals and either the elements of sulfur or phosphorusare inferior not only in their initial activity but durability as well.

As catalyst molders which are suitably used in the preparation of theinvention catalyst, the extrusion molder such as shown in CanadianPatent 812,154 or a stamping type tablet machine, pill machine, etc.,can be used.

According to a preferred embodiment of the invention, the intendedcatalyst is prepared in the following manner. A nickel source and achromium source in which the atomic ratio of nickel to chromium is 1:2 6and the amounts thereof are such that the total content of nickel oxideand chromium oxide in the catalyst to be finally obtained is 10 20 and,as binder, alumina sol and/or a soluble aluminum hydroxidecontainingslurry (or paste) in an amount, based on the weight of the catalyst tobe finally obtained, of 2 20 calculated as alumina and, as a carrier,activated alumina whose particle size distribution is in the range of 2300 microns and average particle diameter is not greater than 110microns are thoroughly mixed and kneaded with a mixer such as, forexample, a kneader to effect the thorough and intimate mutual dispersionof the nickel source and chromium source with the carrier and binder.This is followed by molding the mixture while in its wet state into adesired shape of a diameter 2 8 mm, and preferably 2.5 5 mm, calculatedas spheres, using a catalyst molder such as a stamping type tabletmachine, extrusion molder, pill machine, etc., followed by drying theresulting shaped objects, which, after either calcination for 3 hours ata temperature not exceeding 800C., and preferably for 3 10 hours at atemperature in the range of 400 600C. or without calcination, haveadhered thereto a solution of a palladium salt in an amount, based onthe catalyst to be finally obtained, of 0.01 0.1 by weight, calculatedas palladium, by means of the impregnation or spraying method. Theformed material is then dried at a temperature not exceeding 150C. andthereafter calcined for 3 15 hours at a temperature not exceeding 800C,and preferably for 3 10 hours at a temperature in the range of 400 600C.

In the case of the catalyst prepared as hereinabove described, thenickel and chromium components are uniformly dispersed in the carrieractivated alumina and, since the starting materials are powders, it isporous in character. As a result, it is highly active to hydrocarbonsand is effective in oxidizing and removing the paraffins, which are themost difficulty oxidizable among the hydrocarbons. Furthermore,aluminates do not form easily, and this catalyst does not easily degradeeven though it is exposed to elevated temperatures. The palladiumcomponent of the catalyst possesses especially high activity to carbonmonoxide and also possesses low temperature activity. Therefore, whenthe palladium component is deposited mainly on the surface of the formedmaterial, it is easily warmed up when the engine is started up from itscold state.

In preparing the catalyst of the present invention, a palladium salt inan amount of 0.01 0.1 by weight, calculated as palladium, may be mixedalong with the activated alumina, nickel and chromium sources, andalumina sol and/or a soluble aluminum hydroxide from the outset. Sincein this case the amount of palladium adhereing to the surface of thecatalyst is relatively small, the resulting catalyst is somewhatinferior in its low temperature activity.

The method for preparing the catalyst is characterized in that all thestarting materials are used in either a powder or liquid state. Thecatalyst prepared by such an invention method is more porous than thatprepared by a method in which the catalytic material is adhered to amolded carrier by the impregnation method. Therefore, not only can thereaction gas molecules readily enter into the interior of the catalystbut also the residence time of the gas inside the catalyst is longer,with the consequence that the catalytic effects of the catalyst arepromoted to a still greater degree. For instance, the average porediameter of the catalyst prepared with an extrusion molder in accordancewith the invention method, as determined by the mercury pressuredintroduction method, is 6,000 15,000 A and the pore distribution rangeis 1,000 30,000 A. On the other hand, the catalyst obtained bydepositing similar catalyst substances an activated alumina of sphericalshape has a much smaller average pore diameter value, being usually2,000 A at most, and its pore distribution range is 200 2,500 A. As aresult, its activity to especially hydrocarbons is poor as shown in thehereinafter given examples.

The following examples are given to illustrate the invention more fully,it being understood that these are merely intended in an illustrativesense and not in limitation of the invention.

EXAMPLE 1,

One hundred ninety-seven Grams of finely divided nickel nitrate andgrams of chromic anhydride were added to 584 grams of activated aluminaof a particle size distribution in the range of 5 250 microns andaverage particle diameter of 46 microns and thoroughly mixed. This wasfollowed by the addition of 300 grams of an alumina sol containing ofalumina component, after which the mixture was thoroughly mixed andkneaded. Using an extrusion molder, this mixture was then formed intopellets 3 mm in diameter and about 6 mm in length followed by drying theresulting pellets at about 100C. and calcination for 3 hours at about500C. in air. 500 Grams of these pellets were impregnated with asolution in 150 cc of water of 0.55 gram of palladium nitrate. Thepellets were then dried again at about 100C. and calcined for 3 hours atabout 500C. in air. The atomic ratio was nickel to chromium of the soobtained catalyst was 1:2 and the total weight of nickel oxide andchromium oxide was by weight, while the palladium content was 0.05 byweight. The average pore diameter of this catalyst was 9,000 A and itspore distribution range was 2,000

CONTROL I This control experiment illustrates the case of a catalystwhich does not contain the palladium compound. 98.5 Grams of finelydivided nickel nitrate and 67.5 grams of chromic anhydride were added to292 grams of the finely divided activated alumina of an average particlediameter of 46 microns of Example I and thoroughly mixed. This wasfollowed by the addition of 150 grams of an alumina sol containing 10 ofthe alumina component, after which the mixture was thoroughly mixed andkneaded. This mixture was then formed as in Example I into pelletshaving a diameter of 3 mm and a length of about 6 mm. The pellets werethen dried and calcined as in Example I. The atomic ratio of nickel tochromium of the so obtained catalyst was 1:2 and the total weight ofnickel oxide and chromium oxide was 20 by weight. The average porediameter of this catalyst was 9,000 A and the pore distribution rangewas 2,000 5 18,000 A.

CONTROL II In this control experiment, instead of using a powder aluminaas in the invention method, an alumina carrier previously molded into aspherical form was used.

17.] Grams of nickel nitrate and 1 1.8 Grams of chromic anhydride weredissolved in 80 cc of water, after which the resulting solution was usedand 120 grams of activated alumina carriers 2 4 mm in diameter wereimpregnated with this solution. After drying the impregnated carriers at100C., they were next impregnated with a solution containing 0.145 gramof palladium nitrate followed by drying at 100C. and calcining for 5hours at 500C. The composition of the so obtained catalyst was such thatthe atomic ratio of nickel to chromium was 1:2, the total weight ofnickel oxide and chromium oxide was 10 by weight, and the con tent ofpalladium was 0.05 The average pore diameter of this catalyst was 1,800A, and its pore distribution range was 600 2,500 A.

EXAMPLE II Calcined pellets in which the atomic ratio of nickel tochromium was 1:6 and-the total amount of nickel oxide and chromium oxidewas 20 by weight were prepared by the procedure described in Example I.

Next, palladium in an amount of 0.05 by weight of the pellets wasdeposited'thereon as in Example I followed by drying and calcination ofthe pellets. The average pore diameter of the so obtained pellets was12,000 A, and the pore distribution range was 3,000 21 ,000 A.

EXAMPLE III EXAMPLE IV In this example the palladium was adhered to thepellets by the spraying method.

Calcined pelles in which the atomic ratio of nickel to chromium was 1:4and the total amount of nickel oxide and chromium oxide was 10 by weightwere prepared as in Example I. A solution in 20 cc of water of 0.084gram of palladium chloride was then spraydeposited uniformly onto 100grams of the foregoing pellets. This was followed by again drying andcalcining the pellets as in Example I. The palladium content of the soobtained catalyst was 0.05 %by weight, and its average pore diameter was11,000 A, while the pore distribution range was 2,500 20,000 A.

EXAMPLE V 32.6 Grams of finely divided nickel hydroxide prepared bydrying for 12 hours at 1 10 120C. nickel hydroxide precipitated incustomary manner from an aqueous nickel nitrate solution using NI-I Ol-Iand 420 grams of finely divided chromium nitrate were thoroughly mixedwith 494 grams of finely divided activated alumina of an averageparticle diameter of 46 microns such as used in Example I, after which149 grams of fibrous, soluble boehmite, Baymal (0.714 grams of aluminacontained per gram) and 450 cc of water were added and the mixture wasthoroughly mixed and kneaded with a kneader. The resulting mixture wasthen formed into pellets 3 mm in diameter and about 6 mm in length,using an extrusion molder, followed by drying for about 3 hours at about150C. This was followed by impregnating 20 grams of these pellets with asolution in cc of water of 0.436 gram of palladium nitrate and againdrying at about C., following which the pellets were calcined for 5hours at about 500C. in air. The composition of the so obtained catalystwas such that the atomic ratio of nickel to chromium was *113, the totalamount of nickel oxide and chromium oxide was 15 by weight and thecontent of palladium was 0.05 by weight. The average pore diameter ofthis catalyst was 12,000 A and its pore distribution range was 3,00021,000 A.

EXAMPLE VI 61.8 Grams of a chromium oxide gel prepared by drying for 12hours atl 10 C. chromium hydrox ide preciptiated in customary mannerfrom an aqueous chromium nitrate solution using NI-I OH and 58.2 gramsof nickel nitrate were rendered into a slurry by dispersing ordissolving the same in 160 grams of an alumina sol containing 10alumina. This slurry was introduced to a powder mixture of 294 grams ofactivated alumina of an average particle diameter of 46 microns, such asused in Example I, and 45.4 grams of Baymal and thoroughly mixed andkneaded with a kneader. This mixture was then formed into pellets 3 mmin diameter and about 6 mm in length, using an extrusion molder, afterwhich the pellets were dried and calcined as in Example I. Then 200grams of these pellets were impregnated with a palladium nitratesolution as in Example I, and dried and calcined as in Example I. Theatomic ratio of nickel to chromium of the so obtained catalyst was 1:3,and the total amount of nickel oxide and chromium oxide was by weight,while the palladium content was 0.05 by weight. Further, the averagepore diameter of this catalyst was 10,000 A, and its pore distributionrange was 2,500 19,000 A.

EXAMPLE VII 18.5 Grams of nickel hydroxide prepared by drying for 12hours at 1 10 120C. nickel hydroxide precipitated in customary mannerfrom an aqueous nickel nitrate solution using NH OH and 61.8 grams of achromium oxide gel prepared as in Example VI were slurried by dispersingin 180 grams of an alumina sol containing 10 of alumina. This slurry wasthen introduced to a powder mixture of 297 grams of activated alumina ofan average particle diameter of 46 microns and 77 grams of Baymal andthoroughly mixed and kneaded with a kneader. The mixture was then formeda particle size distribution. range of 5 80 microns and an averageparticle diameter of 37 microns. This mixture was thoroughly mixed andkneaded in a kneader with a mixture of a solution in 20cc of water of1.03 grams of palladium nitrate and 190 grams of an alumina solcontaining 10 of alumina. The resulting mixture was then formed intospherical pellets of about 3.5 mm diameter, using a pill machine,followed by drying at about 100C. and thereafter calcining for 5 hoursat about 500C. in air. The atomic ratio of nickel to chromium of the soobtained catalyst was 1:4, and the total amount of nickel oxide andchromium oxide con tained was 20 by weight, while the palladium contentwas 0.1 by weight. Further, the average pore diameter of this catalystwas 1 1,000 A, and its pore distribution range was 2,000 19,000 A.

EXAMPLE IX The activity of the catalysts obtained in the foregoingExamples I VII and Controls I II was tested in the following manner.

Five cc of each catalyst were packed in a stainless steel reaction tubehaving an inside diameter of 18 mm, and a gas mixture composed of onevolume of CO, 600 ppm of CaHg, 5 volume of O and the rest N was passedthrough the tube at a space velocity of 30,000 hr (150 Nl/hr) at atemperature of 200 500C. When the effluent gas was analyzed by means ofgas chromatography, the rate of conversion of CO to CO (CO conversion)and the rate of conversion of C l-I to CO and H 0 (I-IC conversion) at200, 250, 300, 400 and 500C. were as follows:

CO Conversion (7:)

HC Conversion (71) Experiment 200C. 250C. 300C. 400C. 500C. 200C. 250C.300C. 400C. 500C.

Example I 47.0 98.0 99 I00 I00 0 33 65 92 I00 Control I 3 I7 44 SI 98 920 53 92 I00 Control II I8 87 96 99 I00 0 28 38 75 88 Example II 43 9899 I00 I00 3 37 69 9I I00 Example III 2 67 96 99 I00 3 29 64 95 I00Example IV 85 99 I00 I00 I00 5 33 57 88 I00 Example V 48 88 98 I00 I00 758 87 100 Example VI 57 86 98 I00 I00 2 35 60 88 I00 Example VII 38 9298 99 I00 2 47 79 92 I00 18 98 99 I00 I00 8 3 I 62 87 I00 Example IXinto pellets 3 mm in diameter and about 6 mm in length, and dried andcalcined as in Example I. This was followd by impregnating 200 grams ofthese pellets with a palladium nitrate solution as in Example I followedby drying and calcining as in Example I. The atomic ratio of nickel tochromium of the so obtained catalyst was 1:3, and the total amount ofnickel oxide and chromium oxide contained in the catalyst was 15 byweight, while the palladium content was 0.05 by weight. Further, theaverage pore diameter of this catalyst was 10,000 A, and its poredistribution range was 2,000 19,000 A.

EXAMPLE VIIl In this example the palladium salt was mixed with thecarrier and binder along with the nickel and chromium sources inpreparing the catalyst.

72.2 Grams of finely divided nickel nitrate and 95.4 grams of chromicanhydride were thoroughly mixed with 357 grams of finely dividedactivated alumina of Although good results are demonstrated in both theCO and I-IC conversion in the case of the invention catalyst, theactivity to CO in the case of the catalyst of Control I is notsatisfactory while the activity to I-IC is not good in the case of thecatalyst of Control Il.

EXAMPLE X As representative of the invention catalyst 50 cc of thatobtained in Example I were packed in a stainless steel reaction tubehaving an inside diameter of 30 mm, and the inlet temperature was set at400C. by means of an electric furnace.

Bench test equipment on which was mounted a commerically available6-cylinder gasoline engine of 2,000 cc displacement was used, and theengine was operated at an engine revolution of 2,000 rpm and a boostpressure of 380 mm Hg, using lead-free gasoline. A part of the exhaustgas from this engine and the required amount of air were mixed with ablower and passed over the foregoing catalyst at the rate of 25 litersper minute calculated at room temperature for 100 hours. When the CO andtotal HC (calculated as propane) were analyzed by gas chromatography,the composition of the gas at the inlet was 1.5 2.0 CO, 5.5 6.4 O 130220 ppm HC and the balance CO H O, N etc., whereas the emmision gascontained only 0.01 0.06 CO and 5 18 ppm HC, thus showing a markeddecrease of these gases. The temperature of the catalytic layer was 490564C. during this test. When the conversions were calculated, it was 9799.6 for CO and 90 97 for HC. Further, no decrease in activity was seenwith the passage of time.

EXAMPLE XI A conversion having a catalytic layer whose dimensions bothlengthwise and breadthwise were 160 mm and whose depth was 40 mm waspacked with the catalyst prepared as in Example I. The converter wasthen mounted at a point 1.5 meters from the outlet of the enginemanifold. The exhaust gas was then passed through for 100 hours underthe conditions of 4 mode test procedure prescribed by the Ministry ofTransportation of Japan, using lead-free gasoline. The 4 mode testprocedure is carried out in the following manner. Idling, 40 km per houracceleration 40 km per hour road load cruise and 40 0 km per hourdeceleration operations are repeated, the acceleration from 0 to 40 kmper hour being carried out in 11.5 seconds at this time and thedeceleration from 40 to 0 km per hour being carried out in 7 seconds.The measurement value of the concentration of the exhaust gas obtainedduring the idling is multiplied by a weighting factor of 0.1 l, themeasurement value obtained during the acceleration is multiplied by aweighting factor of 0.35, the measurement value obtained during thecruise is multiplied by a weighting factor of 0.52, and the measurementvalue obtained during the deceleration is multiplied by a weightingfactor of 0.02. These values are totaled and this is designated theaverage exhaust concentration. The engine used in the test was that ofExample X. When the gas entering the converter and that emittedtherefrom were analyzed with a nondispersive infrared gas analyzer, theresults were as follows: Whereas the entering CO averaged 3.0 3.5 andthe entering HC was 200 300 ppm, the CO emitting from the exit averagedinitially 0.03 and after the 100- hour test, 0.12 On the other hand, theHC emitting from the exit was initially 3 ppm and after the 100-hourtest, 5 ppm. The conversions were initially CO 98.5 and HC 98.2 and,after the l00-hour test, CO 96.2 and HC 97.9 The temperature at theentrance to the converter was between 220 and 240C. during the test, andthe temperature of the catalytic layer was from 625 to 665C.

EXAMPLE X A downflow type converter having a catalytic layer 300 mm inlength, 200 mm in width and 35 mm in depth (inside volume 2 liters) waspacked with the catalyst prepared as in Example I. The converter wasthen mounted to a commerically available 4-cylinder engine of 1,600 ccdisplacement at a point 800 mm from the outlet of the engine manifold,the secondary air required being mixed and introduced at the inlet ofthe converter by an air pump. The 7 mode 7 cycle test procedure asprescribed in the U. S. Government Federal Register, vol. 33, No. 108(1968) was then'conducted 9 110 using lead-free gasoline. The engine wasmounted on bench test equipment and as the transmission a threespeedautomatic torque converter was used. For absorbing the power, a 110 KWedic-type electrodynamometer, an inertia flywheel of 0.7 kg-m-sec anddisk brakes were directly coupled. The program control apparatus was,then operated. The analysisof the emission gas was carried out using theMEXA-l8 type analyzer manufactured by Horiba Seisakujo, Japan [analysesof C0, C0 NO and N0 was by means of the nondispersive infrared gasanalyzer (NDIR), and the analysis of HC was by mean of the flameionization analyzer (FID)].

When hot, the concentration at the inlet of the converter of CO was 1925 g/mile and that of BC was 2.1 2.6 g/mile, whereas at the outlet ofthe converter the concentration of CO was initially 1.5 g/mile and thatof HC was initially 0.52 g/mile and, after a 20,000 km run that of COwas 1.8 g/mile and that of BC was 0.63 g/mile. As to the operationalpattern of the durability drive mode of the test, this was carried outin the following manner. Road load runs at 60 km per hour and km perhour were alternately run for two minutes, and at the time of the changein speed the deceleration to 30 km per hour was practiced without fail,following which the acceleration to the next prescribed speed wasimmediately carried out at full throttle.

During the test the inlet temperature of the converter, when hot, was300 400C. and the temperature inside the catalytic layer ranged between440 and 550C.

We claim:

1. A method for preparing a catalyst suitable for use in a catalyticsystem for oxidation of air pollutants in automotive exhaust gases, saidmethod comprising, in combination, the steps of mixing and kneading anickel compound selected from the group consisting of a water-solublenickel salt, nickel hydroxide and nickel oxide and a chromium compoundselected from the group consisting of a water-soluble chromium salt,chromium acid, chromium hydroxide and chromium oxide, the atomic ratioof nickel to chromium being 1 l-12, and the amounts of said nickelcompound and chromium compound being such that the total weight ofnickel oxide and chromium oxide contained in the final catalyst is 530%, and, as a binder, a member selected from the group consisting of analumina sol and a soluble aluminum hydroxide, said binder being used inan amount of 2 20%, calculated as alumina, based on the weight of thefinal catalyst and, as a carrier, activated alumina having a particlesize distribution in the range of 2 300 microns and an average particlediameter of not greater than microns; molding the resulting mixture witha catalyst molder into a desired shape; drying the molded material at atemperature not exceeding C; impregnating the dried molded material witha solution of a water-soluble palladium salt in an amount of 0.010.l%,-calculated as palladium, based on the weight of the finalcatalyst; drying the impregnated material at a temperature not exceeding150C; and thereafter calcining the dried material at a temperature notexceeding 800C. for 3 1 5 hours to prepare the final catalyst.

2. The method of claim 1 wherein said nickel compound is a solution of asoluble nickel salt.

3. The method of claim 1 wherein said nickel compound is a slurry of afinely divided, difficulty soluble nickel compound of an averageparticle diameter not greater than 110 microns.

4. The method of claim 1 wherein said chromium compound is a solution ofa soluble chromium salt.

5. The method of claim 1 wherein said chromium compound is a slurry of afinely divided, difficulty soluble chromium compound of an averageparticle diameter no greater than 1 10 microns.

6. The method of claim 1 wherein said nickel salt is selected from thegroup consisting of the acetate, bromide, chloride, nitrate, oxalate,formate and carbonate of nickel.

7. The method of claim 1 wherein said chromium salt is selected from thegroup consisting of ammonium chromate, ammonium dichromate, chromiumnitrate, chromium acetate, chromium chloride, and chromium carbonate.

8. The method of claim 1 wherein the palladium salt is selected from thegroup consisting of the bromide, chloride and nitrate of palladium.

9. A method for preparing a catalyst suitable for use in a catalyticsystem for oxidation of air pollutants in automotive exhaust gases, saidmethod comprising, in combination, the steps of mixing and kneading anickel compound selected from the group consisting of a water-solublenickel salt, nickel hydroxide and nickel oxide and a chromium compoundselected from the group consisting of a water-soluble chromium salt,chromic acid, chromium hydroxide and chromium oxide, the atomic ratio ofnickel to chromium being 1 l 12, and the amounts of said nickel compoundand chromium compound being such that the total weight of nickel oxideand chromium oxide contained in the final catalyst is 30%, and, as abinder, a member selected from the group consisting of an alumina soland a soluble aluminum hydroxide, said binder being used in an amount of2 20%, calculated as alumina, based on the weight of the final catalyst,and, as a carrier, activated alumina having a particle size distributionin the range of 2 300 microns and an average particle diameter of notgreater than 110 microns, and a watersoluble palladium salt in an amountof 0.01 0. 1%, calculated as palladium, based on the weight of the finalcatalyst; molding the resulting mixture with a catalyst molder with adesired shape; drying the molded mate rial at a temperature notexceeding 150C.; and thereafter calcining the dried material for 3 15hours at a temperature not exceeding 800C to prepare the final catalyst.

10. The method of claim 9 wherein said nickel compound is a solution ofa soluble nickel salt.

11. The method of claim 9 wherein said nickel compound is a slurry of afinely divided, difficulty soluble nickel compound of an averageparticle diameter not greater than 1 10 microns.

12. The method of claim 9 wherein said chromium compound is a solutionof a soluble chromium salt.

13. The method of claim 9 wherein said chromium compound is a slurry ofa finely divided, difficulty soluble chromium compound of an averageparticle diameter not greater than 110 microns.

14. The method of claim 9 wherein said nickel salt is selected from thegroup consisting of the acetate, bromide, chloride, nitrate, oxalate,formate and carbonate of nickel.

15. The method of claim 9 wherein said chromium salt is selected fromthe group consisting of ammonium chromate, ammonium dichromate, chromiumnitrate, chromium acetate, chromium chloride, and chromium carbonate.

16. The method of claim 9 wherein said palladium salt is selected fromthe group consisting of the bromide, chloride and nitrate of palladium.

17. A method for preparing a catalyst of an average pore diameter of6,000-l 5,000 A, which is suitable for use in a catalytic system foroxidation of air pollutants in automotive exhaust gases, said methodcomprising, in combination, the steps of mixing and kneading a nickelcompound selected from the group consisting of a water-soluble nickelsalt, nickel hydroxide and nickel oxide and a chromium compound selectedfrom the group consisting of a water-soluble chromium salt, chromicacid, chromium hydroxide and chromium oxide, the atomic ratio of nickelto chromium being 1 l-12, and the amounts of said nickel compound andchromium compound being such that the total weight of nickel oxide andchromium oxide contained in the final catalyst is 5 30%, and, as abinder, a member selected from the group consisting of an alumina soland a soluble aluminum hydroxide, said binder being used in an amount of2-20%, calculated as alumina, based on the weight of the final catalyst,and, as a carrier, activated alumina having a particle size distributionin the range of 2-300 microns and an average particle diameter of notgreater than 1 10 microns; molding the resulting mixture with a catalystmolder into a desired shape; drying the molded material at a temperaturenot exceeding l50C,; impregnating the dried molded material with asolution of a water-soluble palladium salt in an amount of 0.01 0.1%,calculated as palladium, based on the weight of the final catalyst;drying the impregnated material at a temperature not exceeding C; andthereafter calcining the dried material at a temperature not exceeding800C. for 3-15 hours to prepare the final catalyst.

18. A method for preparing a catalyst of an average pore diameter of6,000-1 5,000 A, which is suitable for use in a catalytic system foroxidation of air pollutants in automotive exhaust gases, said methodcomprising, in combination, the steps of mixing and kneading a nickelcompound selected from the group consisting of a water-soluble nickelsalt, nickel hydroxide and nickel oxide and a chromium compound selectedfrom the group consisting of a water-soluble chromium salt, chromicacid, chromium hydroxide and chromium oxide, the atomic ratio of nickelto chromium being 1 l-l2, and the amounts of said nickel compound andchromium being such that the total weight of nickel oxide and chromiumoxide contained in the final catalyst is 530%, and, as a binder, amember selected from the group consisting of an alumina sol and asoluble aluminum hydroxide, said binder being used in an amount of2-20%, calculated as alumina, based on the weight of the final catalyst,and, as a carrier, activated alumina having a particle size distributionin the range of 2300 microns and an average particle diameter of notgreater than 1 10 microns, and a water-soluble palladium salt in anamount of 0.01 0.1%, calculated as palladium, based on the weight of thefinal catalyst; molding the resulting mixture with a catalyst molderinto a desired shape; drying the molded material at a temperature notexceeding 150C.;.and thereafter calcining the desired material for 3-l5hours at a temperature not exceeding 800C. to prepare the finalcatalyst.

19. A catalyst of an average pore diameter of 6,000 15,000 A obtained bythe method of claim 17, said catalyst being suitable for use in acatalytic system for oxidation of air pollutants in automotive exhaustgases.

20. A catalyst of an average pore diameter of 6,000l5,000 A obtained bythe method of claim 18, said catalyst being suitable for use in acatalytic system for oxidation of air pollutants in automotive exhaustgases.

21. A method for preparing a catalyst suitable for use in catalyticsystem for oxidation of air pollutants in automotive exhaust gases, saidmethod comprising, in combination, the steps of mixing and kneading anickel compound selected from the group consisting of a water-solublenickel salt, nickel hydroxide and nickel oxide and a chromium compoundselected from the group consisting of a water-soluble chromium salt,chromic acid, chromium hydroxide and chromium oxide, the atomic ratio ofnickel to chromium being 1 l-l2, and the amounts of said nickel compoundand chromium compound being such that the total weight of nickel oxideand chromium oxide contained in the final catalyst is 5 30%, and, as abinder, a member selected from the group consisting of an aluminum soland a soluble aluminum hydroxide, said binder being used in an amount of2 20%, calculated as alumina, based on the weight of the final catalystand, as a carrier, activated alumina having a particle size distributionin the range of 2 300 microns and an average particle diameter of notgreater than 1 microns; molding the resulting mixture with a catalystmolder into a desired shape; drying the molded material at a temperaturenot exceeding 150C.; calcining the dried material at a temperature notexceeding 800C.; impregnating the calcined molded material with asolution of a watersoluble palladium salt in an amount of 0.01 0.1%,calculated as palladium, based on the weight of the final catalyst;drying the impregnated material at a temperature not exceeding 150C; andthereafter calcining the dried material at a temperature not exceeding800C. for 3 hours to prepare the final catalyst.

22. A method for preparing a catalyst of an average the group consistingof a water-soluble salt, chromium acid, chromium hydroxide and chromiumoxide, the atomic ratio of nickel to chromium being 1 1-12, and theamounts of said nickel compound and chromium compound being such thatthe total weight of nickel oxide and chromium oxide contained in thefinal catalyst is 5 30%, and, as a binder, a member selected from thegroup consisting of an alumina sol and a soluble aluminum hydroxide,said binder being used in an amount of 2-20%, calculated as alumina,based on the weight of the final catalyst, and, as a carrier, activatedalumina being a particle size distribution in the range of 2-300 micronsand an average particle diameter of not greater than microns; moldingthe resulting mixture with a catalyst molder into a desired shape;drying the molded material at a temperature not exceeding C; calciningthe dried material at a temperature not exceeding 800C.; impregnatingthe calcined molded material with a solution of a watersoluble palladiumsalt in an amount of 0.01 0.1%, calculated as palladium based on theweight of the final catalyst, drying the impregnated material at atemperature not exceeding 150C; and thereafter calcining the driedmaterial at a temperature not exceeding 800C. for 3-l5 hours to preparethe final catalyst.

23. A catalyst suitable for use in a catalytic system for oxidation ofair pollutants in automotive exhaust gases prepared by the method ofclaim 1.

24. A catalyst suitable for use in a catalytic system for oxidation ofair pollutants in automotive exhaust gases prepared by the method ofclaim 9.

25. A catalyst suitable for use in a catalytic system for oxidation ofair pollutants in automotive exhaust gases prepared by the method ofclaim 21.

26. A catalyst suitable for use in a catalytic system for oxidation ofair pollutants in automotive exhaust gases prepared by the method ofclaim 22.

- UNITED STA'lES PATENT OFFECE CEER'llFlfiATE F CURECHGN Patent No.3,787 333 I Dated January 22, 1974 Shoichi ICHIHARA ET AL Inventor(s) Itis certified that error appears in the above-identified patent I andthat said Latte-re Patent are hereby corrected as shown below:

In the Heading, insert peatetttees elaim for priority as follows: MClaims priority, epplieatiom Japan, November 18, 1970,.Nm mime/7e M Col6, line 24-: eaneel "pelles" and insert pellets Claim 18, line .28:cancel desired and insert M dried This certificate supersedesCertificate of Correction issue May 28 1974 Signed and sealed this 8thday of October" 197% (SEAL) Attest:

MCCQY Mo GIBSON JR. Attesting Officer 60- MARSHALL DANN Commissioner ofPatents .J 0-00 104398 FOR P I J uscomm-oc 60376-P69 U75, GOIERNMENKPRINTING OFFICE: [9559 O-355-334

2. The method of claim 1 wherein said nickel compound is a solution of asoluble nickel salt.
 3. The method of claim 1 wherein said nickelcompound is a slurry of a finely divided, difficulty soluble nickelcompound of an average particle diameter not greater than 110 microns.4. The method of claim 1 wherein said chromium compound is a solution ofa soluble chromium salt.
 5. The method of claim 1 wherein said chromiumcompound is a slurry of a finely divided, difficulty soluble chromiumcompound of an average particle diameter no greater than 110 microns. 6.The method of claim 1 wherein said nickel salt is selected from thegroup consisting of the acetate, bromide, chloride, nitrate, oxalate,formate and carbonate of nickel.
 7. The method of claim 1 wherein saidchromium salt is selected from the group consisting of ammoniumchromate, ammonium dichromate, chromium nitrate, chromium acetate,chromium chloride, and chromium carbonate.
 8. The method of claim 1wherein the palladium salt is selected from the group consisting of thebromide, chloride and nitrate of palladium.
 9. A method for preparing acatalyst suitable for use in a catalytic system for oxidation of airpollutants in automotive exhaust gases, said method comprising, incombination, the steps of mixing and kneading a nickel compound selectedfrom the group consisting of a water-soluble nickel salt, nickelhydroxide and nickel oxide and a chromium compound selected from thegroup consisting of a water-soluble chromium salt, chromic acid,chromium hydroxide and chromium oxide, the atomic ratio of nickel tochromium being 1 : 1 - 12, and the amounts of said nickel compound andchromium compound being such that the total weight of nickel oxide andchromium oxide contained in the final catalyst is 5 - 30%, and, as abinder, a member selected from the group consisting of an alumina soland a soluble aluminum hydroxide, said binder being used in an amount of2 - 20%, calculated as alumina, based on the weight of the finalcatalyst, and, as a carrier, activated alumina having a particle sizedistribution in the range of 2 - 300 microns and an average particlediameter of not greater than 110 microns, and a water-soluble palladiumsalt in an amount of 0.01 - 0.1%, calculated as palladium, based on theweight of the final catalyst; molding the resulting mixture with acatalyst molder with a desired shape; drying the molded material at atemperature not exceeding 150*C.; and thereafter calcining the driedmaterial for 3 - 15 hours at a temperature not exceeding 800*C toprepare the final catalyst.
 10. The method of claim 9 wherein saidnickel compound is a solution of a soluble nickel salt.
 11. The methodof claim 9 wherein said nickel compound is a slurry of a finely divided,difficulty soluble nickel compound of an average particle diameter notgreater than 110 microns.
 12. The method of claim 9 wherein saidchromium compound is a solution of a soluble chromium salt.
 13. Themethod of claim 9 wherein said chromium compound is a slurry of a finelydivided, difficulty soluble chromium compound of an average particlediameter not greater than 110 microns.
 14. The method of claim 9 whereinsaid nickel salt is selected from the group consisting of the acetate,bromide, chloride, nitrate, oxalate, formate and carbonate of nickel.15. The method of claim 9 wherein said chromium salt is selected fromthe group consisting of ammonium chromate, ammonium dichromate, chromiumnitrate, chromium acetate, chromium chloride, and chromium carbonate.16. The method of Claim 9 wherein said palladium salt is selected fromthe group consisting of the bromide, chloride and nitrate of palladium.17. A method for preparing a catalyst of an average pore diameter of6,000-15,000 A, which is suitable for use in a catalytic system foroxidation of air pollutants in automotive exhaust gases, said methodcomprising, in combination, the steps of mixing and kneading a nickelcompound selected from the group consisting of a water-soluble nickelsalt, nickel hydroxide and nickel oxide and a chromium compound selectedfrom the group consisting of a water-soluble chromium salt, chromicacid, chromium hydroxide and chromium oxide, the atomic ratio of nickelto chromium being 1 : 1-12, and the amounts of said nickel compound andchromium compound being such that the total weight of nickel oxide andchromium oxide contained in the final catalyst is 5 - 30%, and, as abinder, a member selected from the group consisting of an alumina soland a soluble aluminum hydroxide, said binder being used in an amount of2-20%, calculated as alumina, based on the weight of the final catalyst,and, as a carrier, activated alumina having a particle size distributionin the range of 2-300 microns and an average particle diameter of notgreater than 110 microns; molding the resulting mixture with a catalystmolder into a desired shape; drying the molded material at a temperaturenot exceeding 150*C,; impregnating the dried molded material with asolution of a water-soluble palladium salt in an amount of 0.01 - 0.1%,calculated as palladium, based on the weight of the final catalyst;drying the impregnated material at a temperature not exceeding 150*C.;and thereafter calcining the dried material at a temperature notexceeding 800*C. for 3-15 hours to prepare the final catalyst.
 18. Amethod for preparing a catalyst of an average pore diameter of6,000-15,000 A, which is suitable for use in a catalytic system foroxidation of air pollutants in automotive exhaust gases, said methodcomprising, in combination, the steps of mixing and kneading a nickelcompound selected from the group consisting of a water-soluble nickelsalt, nickel hydroxide and nickel oxide and a chromium compound selectedfrom the group consisting of a water-soluble chromium salt, chromicacid, chromium hydroxide and chromium oxide, the atomic ratio of nickelto chromium being 1 : 1-12, and the amounts of said nickel compound andchromium being such that the total weight of nickel oxide and chromiumoxide contained in the final catalyst is 5-30%, and, as a binder, amember selected from the group consisting of an alumina sol and asoluble aluminum hydroxide, said binder being used in an amount of2-20%, calculated as alumina, based on the weight of the final catalyst,and, as a carrier, activated alumina having a particle size distributionin the range of 2-300 microns and an average particle diameter of notgreater than 110 microns, and a water-soluble palladium salt in anamount of 0.01 - 0.1%, calculated as palladium, based on the weight ofthe final catalyst; molding the resulting mixture with a catalyst molderinto a desired shape; drying the molded material at a temperature notexceeding 150*C.; and thereafter calcining the desired material for 3-15hours at a temperature not exceeding 800*C. to prepare the finalcatalyst.
 19. A catalyst of an average pore diameter of 6,000 - 15,000 Aobtained by the method of claim 17, said catalyst being suitable for usein a catalytic system for oxidation of air pollutants in automotiveexhaust gases.
 20. A catalyst of an average pore diameter of6,000-15,000 A obtained by the method of claim 18, said catalyst beingsuitable for use in a catalytic system for oxidation of air pollutantsin automotive exhaust gases.
 21. A metHod for preparing a catalystsuitable for use in catalytic system for oxidation of air pollutants inautomotive exhaust gases, said method comprising, in combination, thesteps of mixing and kneading a nickel compound selected from the groupconsisting of a water-soluble nickel salt, nickel hydroxide and nickeloxide and a chromium compound selected from the group consisting of awater-soluble chromium salt, chromic acid, chromium hydroxide andchromium oxide, the atomic ratio of nickel to chromium being 1 : 1-12,and the amounts of said nickel compound and chromium compound being suchthat the total weight of nickel oxide and chromium oxide contained inthe final catalyst is 5 - 30%, and, as a binder, a member selected fromthe group consisting of an aluminum sol and a soluble aluminumhydroxide, said binder being used in an amount of 2 - 20%, calculated asalumina, based on the weight of the final catalyst and, as a carrier,activated alumina having a particle size distribution in the range of2 - 300 microns and an average particle diameter of not greater than 110microns; molding the resulting mixture with a catalyst molder into adesired shape; drying the molded material at a temperature not exceeding150*C.; calcining the dried material at a temperature not exceeding800*C.; impregnating the calcined molded material with a solution of awater-soluble palladium salt in an amount of 0.01 - 0.1%, calculated aspalladium, based on the weight of the final catalyst; drying theimpregnated material at a temperature not exceeding 150*C.; andthereafter calcining the dried material at a temperature not exceeding800*C. for 3 - 15 hours to prepare the final catalyst.
 22. A method forpreparing a catalyst of an average pore diameter of 6,000-15,000 A,which is suitable for use in a catalytic system for oxidation of airpollutants in automotive exhaust gases, said method comprising, incombination, the steps of mixing and kneading a water-soluble nickelcompound selected from the group consisting of a nickel salt, nickelhydroxide and nickel oxide and a chromium compound selected from thegroup consisting of a water-soluble salt, chromium acid, chromiumhydroxide and chromium oxide, the atomic ratio of nickel to chromiumbeing 1 : 1-12, and the amounts of said nickel compound and chromiumcompound being such that the total weight of nickel oxide and chromiumoxide contained in the final catalyst is 5 -30%, and, as a binder, amember selected from the group consisting of an alumina sol and asoluble aluminum hydroxide, said binder being used in an amount of2-20%, calculated as alumina, based on the weight of the final catalyst,and, as a carrier, activated alumina being a particle size distributionin the range of 2-300 microns and an average particle diameter of notgreater than 110 microns; molding the resulting mixture with a catalystmolder into a desired shape; drying the molded material at a temperaturenot exceeding 150*C.; calcining the dried material at a temperature notexceeding 800*C.; impregnating the calcined molded material with asolution of a water-soluble palladium salt in an amount of 0.01 - 0.1%,calculated as palladium based on the weight of the final catalyst,drying the impregnated material at a temperature not exceeding 150*C.;and thereafter calcining the dried material at a temperature notexceeding 800*C. for 3-15 hours to prepare the final catalyst.
 23. Acatalyst suitable for use in a catalytic system for oxidation of airpollutants in automotive exhaust gases prepared by the method ofclaim
 1. 24. A catalyst suitable for use in a catalytic system foroxidation of air pollutants in automotive exhaust gases prepared by themethod of claim
 9. 25. A catalyst suitable for use in a catalytic systemfor oxidation of air polLutants in automotive exhaust gases prepared bythe method of claim
 21. 26. A catalyst suitable for use in a catalyticsystem for oxidation of air pollutants in automotive exhaust gasesprepared by the method of claim 22.